Overview
Twilio SendGrid provides Email view tracking with the open engagement Event Webhook. This webhook can be helpful to see if a message has been opened or viewed, and can enable you to build advanced analytics.
What You Need To Know
At this time, SendGrid does not differentiate unique opens from regular open engagement event responses; these are both classified under the singular open event. Users looking to track unique open events will want to setup logic in your application that parses the first open event for each specific message ID. It is possible to see unique opens within the SendGrid UI as seen here.
Additional Information
For full details on how Event webhook callbacks work, see Event Webhook Reference (SendGrid Docs).